This invention relates generally to a borehole contacting apparatus for mounting on a bottom hole assembly of a drill string. More specifically, the invention is directed to a roller reamer apparatus which has a self-tightening mounting system with self-lubricating bearings and which is easily replaced with minimum down time during drilling operations.
It is well known in the art that roller cutters may be used as reamers on the bottom of a drill string for enlarging the borehole. Known U.S. Patents disclosing roller reamers are as follows: U.S. Pat. Nos. 2,122,763; 2,172,762; 2,189,033; 2,189,035; 2,189,036; 2,189,037; 2,199,693; 2,218,743; 2,260,366; 2,306,492; 2,695,771; 2,716,020; 3,303,900; 3,306,381; 3,627,068; and 3,907,048. As shown by the above listed patents, numerous attempts have been made to obtain a rigid secure fit of a roller reamer with a reamer body, while at the same time allowing ease of removal and replacement of the shafts or spindles and roller.
In particular, U.S. Pat. No. 2,122,763 issued to Smith discloses a mounting system and the present invention includes a self-tightening locking system which is an improvement thereof. Smith discloses locking means, consisting of bolts 19 which connect wedge plates 12 that have been driven into engagement with bearing blocks 7. The wedge plate 12 comprises three angled surfaces to enable it to be inserted radially with minimum axial movement. The rib 13 on bearing block 7 prevents axial movement of the block in the mounting slot thereby preventing any self-tightening of the locking means induced by the thrust of the cutters and frictional engagement of the locking means with the borehole.
An attempt to provide a structure which uses no bolts or threaded parts in mounting the roller reamer to the reamer body is shown in U.S. Pat. No. 2,189,036 issued to Jones, U.S. Pat. No. 2,306,492 issued to W. B. Noble, and U.S. Pat. No. 3,189,037 issued to Harrington. A device in common use today, which is manufactured by the Drilco Division of Smith International, Inc., utilizes a cross pin to retain a bearing block which supports a reamer pin. The Drilco device does not utilize a wedge, such as the wedge 11 shown by Noble or the wedge 18 shown by Harrington, and the cross pin it uses is a spring pin which is driven into an upper bearing block to retain the main reamer pin and reamer cutter. A similar design is shown in U.S. Pat. No. 3,303,900. The reamer pin in the Drilco device does not rotate, but rather is locked into position so that the reamer cutter rotates relative to the supporting reamer pin. Cap screws have been used as a secondary locking device for locking the reamer pins from rotation relative to the bearing blocks.
Certain problems may arise with the use of a locking cross pin. For instance, if the pin becomes broken for any reason, forces on the bearing blocks may tend to cause them to loosen. Also, locking cross pins such as shown in the Drilco device require accurate alignment of the bearing block aperture which receives the locking cross pin with grooves in the reamer body. Similar problems occur if the spring ring of Harrington breaks or becomes dislodged.
Other known patents are U.S. Pat. Nos: 3,818,999; 3,370,657; 2,973,996; 2,288,124; 1,062,841; 3,856,096; 3,680,647; 3,938,853; 3,445,144; 3,799,279; 2,084,421; 1,810,030; and 2,864,586.
So far as known, a problem has existed with wearing between the bearing surfaces which include the interior cylindrical surface of the reamer cutter and the outer cylindrical surface of the reamer pin. Lubrication systems are disclosed in U.S. Pat. No. 3,907,048 issued to Gray and U.S. Pat. No. 3,303,900 issued to Kloesel, et al. In practice the bearing surfaces may be worn out long before the cutting surfaces of the reamer cutter since it has been a common practice to use tungsten carbide inserts to reduce wear of the roller cutter. It has also been a practice to rotate the stationary reamer pin 180.degree. in the bearing block since the pressure of the reamer cutter against the well bore tends to cause excess wear on the outer facing surface of the reamer pin. The same wearing problems would be present if the reamer pin rotated in the bearing blocks and the reamer cutter was affixed to the reamer pin. It is therefore apparent that the most important aspect of mounting reamer cutters in a reamer body is that they be mounted as firmly as possible to prevent any possibility of play between the parts constituting the mounting during the operation of the reamer.
It is thus desirable to provide a securing means for a reamer pin bearing block which will securely retain the bearing block within a slot in the reamer body and which can be easily removed for replacement of the reamer cutter. It is important to provide secure locking of the retaining means for the bearing blocks so that pulling into and out of the well bore will not loosen the bearing blocks, while at the same time allowing replacement of worn parts without difficulties. It is also important to protect the bearing surfaces which provide the rotation of the reamer cutter so that the bearing surfaces will permit longer use of the cutting surfaces on the reamer cutter.
As shown by the above patents, several attempts have been made over many years to provide a suitable mounting means and also to protect the bearings. Despite the many attempts, it is believed that the present invention overcomes many of the problems for which a solution has been sought for many years. The reamer assembly is safely and securely mounted, yet it can be simply replaced. The life of the bearing surfaces is increased which increases drilling efficiency.